The present invention relates to a liquid discharge head for discharging liquid, such as an ink jet head for discharging ink, and a manufacturing method thereof.
Conventionally, as an ink jet head to be used in an ink jet type recording apparatus, the ink jet head having a piezoelectric element is known. The piezoelectric element is constituted so that a piezoelectric layer, two electrode layers and a diaphragm layer are laminated (in some piezoelectric elements, the diaphragm layer serves also as one electrode layer). The piezoelectric layer is made of lead zirco-titanate (PTZ) or the like. The electrode layers are provided on both surfaces of the piezoelectric layer in a thickness direction. The diaphragm layer is provided on one of the electrode layers. When voltage is applied to between the electrode layers and a piezoelectric element expands and contracts to a direction vertical to a laminating direction (thickness direction), the expansion and contraction is constrained by the diaphragm layer so that the piezoelectric element is deflected towards an ink chamber into a convex shape so as to be deformed. Pressure is generated in the ink chamber due to the deflective deformation, and the pressure discharges the ink in the ink chamber from a nozzle hole connected with the ink chamber to the outside.
As a method for manufacturing the above ink jet head, for example, Japanese Patent Application Laid-Open No. 10-286953 (1998) suggests a method for forming one electrode film of both electrodes (individual electrode film), a piezoelectric film, the other electrode film (common electrode film) and a diaphragm film successively on a substrate made of MgO by means of sputtering or the like, and aligning and jointing an ink chamber member having an ink chamber hole for composing an ink chamber to the diaphragm film of the piezoelectric element using an adhesive, and removing the deposit substrate by means of etching. According to this manufacturing method, the respective layers are formed on the substrate having a size for a plurality of ink jet heads so that many compact ink jet heads can be manufactured together.
In a method for manufacturing an ink jet head disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-47626, a monocrystal silicon substrate is worked so as to be an ink chamber member, and a piezoelectric element is formed directly on the substrate without using an adhesive.
As a method for forming the ink chamber member, for example, Japanese Patent Application Laid-Open No. 9-300634 (1997) discloses a method for forming the ink chamber member directly on a diaphragm according to electroforming (electroplating) using a dry film resist made of a photosensitive material as a mold.
In recent years, a liquid discharge head having the same structure as the ink jet head, which discharges various kinds of liquid instead of ink, is known. For example, in Japanese Patent Application Laid-Open No. 2001-324505, a biopolymer solution of DNA, protein or the like is discharged from a nozzle hole of the liquid discharge head onto a substrate, so that a biochip is manufactured by an ink jet system.
In the case where the liquid discharge head for discharging the liquid such as ink like the ink jet head is manufactured, the method disclosed in Japanese Patent Application Laid-Open No. 10-286953 (1998) requires the step of jointing a liquid chamber member (corresponding to the ink chamber member of the ink jet head) to a diaphragm film using an adhesive. In the method disclosed in Japanese Patent Application Laid-Open No. 2001-47626, since Young's modulus of silicon is 160 GPa which is very low, when the nozzle and the liquid chamber (ink chamber) are arranged with high density, crosstalk (the discharge properties change due to influence of the diaphragm layer and vibration of liquid in another liquid chambers) easily occurs between plural liquid chambers (particularly adjacent liquid chambers).
In order that the joint step is eliminated and the liquid chamber member is made of a material with high Young's modulus, as disclosed in Japanese Patent Application Laid-Open No. 9-300634 (1997), it is considered that the liquid chamber member is formed on the diaphragm layer by the electroforming.
The electroforming, however, causes a problem such that dispersion of a thickness of the liquid chamber member becomes large. For this reason, in the case where the piezoelectric element is formed on the substrate with large area for enabling the many liquid discharge heads to be manufactured together and the liquid chamber member is formed on the piezoelectric element, the thickness of the liquid chamber member is greatly different between a portion corresponding to a peripheral edge and a portion corresponding to a center of the substrate. As a result, in the case where the liquid chamber member is divided into individual liquid discharge heads, the liquid discharge properties such as a liquid discharge speed and the like differ between the liquid discharge heads. It is, therefore, very difficult to mass-produce the liquid discharge heads using the electroforming.